This invention relates generally to apparatus for inserting drainage wicks into the earth, and more specifically to an improved drive arrangement for positively engaging and driving the wick-carrying tube into the earth.
A well-known technique for preparing soil that has a high moisture content, such as wet clay for example, is to drive into the soil a drainage wick that penetrates deep into the soil, with the top end of the wick maintained above the surface of the soil. The drainage wick is formed of any suitable material which is water permeable so that the water in the soil can permeate the walls of the drainage wick and flow upwardly therein to the surface of the soil as a result of pressures in the soil beneath the surface thereof. The inherent pressures in the soil may be enhanced by putting a layer of sand on top of the wet soil so that the weight of the sand will assist in forcing the water into, and upwardly through, the drainage wick, where it can be readily dispersed.
Since the drainage wick is generally flexible, it must be carried into the ground by utilizing a rigid insertion tubeformed of a suitable metal, and this insertion tube is forcibly driven into the soil, and then pulled out of the soil, by any one of different known drive systems. For example, in Dutch Patent No. 7,707,303, there is disclosed a drive arrangement which uses a vibratory driver that engages the top portion of the insertion tube for driving the bottom end of the insertion tube into the earth. In Cortlever U.S. Pat. No. 4,755,080, a combination of hydraulic cylinders and a cable drive that engages the insertion tube at the upper end thereof is utilized, and a somewhat similar hydraulic motor and chain drive is disclosed in Thorsell U.S. Pat. No. 3,891,186. In Van den Berg U.S. Pat. No. 4,166,508, the disclosed drive arrangement includes flexible steel tubes that are driven into the ground with the drainage wick therein, utilizing rotating drums. It is also known to combine two of the above-described drives in a single installation, such as combining a vibratory driver with a chain or cable drive fixed to the top of the insertion tube. In generally, most of these prior art arrangements engage and drive the insertion tube at the top end thereof, and this arrangement usually requires a heavier boom structure for supporting the insertion tube and the drive arrangement therefor, whereby the overall weight of the system is increased, as well as the cost and maintenance of the system.
It is also known that the insertion tube can be driven into the earth utilizing a pair of friction rollers positioned just above the surface of the earth, these rollers being formed of a material that will frictionally engage the side walls of the insertion tube disposed therebetween with the frictional engagement between the rollers and the insertion tube driving the insertion tube into the ground. While this arrangement overcomes some of the disadvantages of the top drive systems discussed above, it also has several disadvantages. More specifically, since these drainage wick insertion systems usually operate in an environment that includes high moisture content and wet soil, the frictional engagement between the sides of the insertion tube and the friction rollers can be significantly diminished by the presence of moisture and mud between the engaging surfaces of these elements, and the moisture and mud can act as a lubricant that results in an improper and insufficient driving force being applied to the insertion tube. Also, since the wet soil is abrasive in nature, its presence between the engaging surfaces of the friction rollers and the insertion tube can cause excessive wear of the friction rollers. Finally, in these systems, the friction rollers must be placed on opposite sides of the insertion tube and urged thereagainst with a sufficient force to create the necessary frictional purchase to drive the insertion tube into the ground, all of which imposes stress on the insertion tube and may require strengthening thereof through the use of heavier metal since the positioning of the friction rollers generally eliminates the possibility of strengthening the insertion tubes using less expensive strengthening ribs.
In accordance with the present invention, apparatus for inserting drainage wicks is provided which overcomes or alleviates the above-described drawbacks of known apparatus.